Much of Europe's ancient times (800 to 1,300 AD) have been embellished by the ruling class. Life was enough to kill most everyone by the age of 30. The logistics of arming, organizing, training, feeding, clothing, and moving vast armies about back then was impossible. Plague, various viruses, bacterial and fungal infections, and starvation was common living.
Every power which tried eventually suffered the same fate. They collapsed under their own draw-down on resources directly proportionate to distance from homelands.